A pre-alignment operation has been performed in various procedures of a semiconductor wafer processing to align the semiconductor wafer to a predetermined direction prior to main processing steps.
Conventional pre-alignment technology performed by an inspection apparatus prior to electrical characteristic inspection of a semiconductor wafer, is disclosed, for example, in Japanese Patent Application Laid-Open No. 2008-078210. The inspection apparatus includes a loader chamber that loads/unloads the semiconductor wafer, and a prober chamber that conducts electrical characteristic inspection of the semiconductor wafer. Conventional pre-alignment processing is performed in the loader chamber using a pre-alignment mechanism while the semiconductor wafer is being transferred from the loader chamber to the prober chamber, prior to the electrical characteristic inspection of the semiconductor wafer in the prober chamber. The description for a conventional pre-alignment method will be followed.
Conventional pre-alignment mechanism includes a rotatable table for mounting a semiconductor wafer thereon, and an optical detection unit for optically detecting orientation plats or notches (hereinafter notches) formed around an outer periphery of the semiconductor wafer. To perform a pre-alignment of the semiconductor wafer using the pre-alignment mechanism, the semiconductor wafer housed at a cassette located in a load port is transferred to the rotatable table of the pre-alignment mechanism by a wafer transfer mechanism, and the rotatable table where the wafer is mounted is rotated at least one turn. During that time, position data are detected based on the notches of the outer periphery of the semiconductor wafer, by an optical detection unit, and an eccentric value between a center of the semiconductor wafer and a center of the rotatable table is acquired based on the position data. Subsequently, a positional deviation of the semiconductor wafer on the rotatable table is corrected by a wafer transfer mechanism based on the eccentric value, and the position data of the semiconductor wafer are acquired one more time by the optical detection unit. Then the pre-alignment is terminated by aligning the notches of the semiconductor wafer to a predetermined direction. In the series of operations, the rotation operation is performed at least twice by the rotatable table for each semiconductor wafer.
However, in the conventional pre-alignment technology, the position data of the semiconductor wafer needs to be acquired at least twice for each semiconductor wafer while transferring the semiconductor wafer so that the pre-alignment process takes a relatively long time. As a result, an overall transfer time of the semiconductor wafer tends to take longer.